Ara (The Altar) commemorates the altar on
which sacrifices were made to the gods, in both Greek and Roman times. The
Romans called it Ara Centauri, considering it to represent the
altar Centaurus used (perhaps to sacrifice Lupus, the Wolf).
The constellation is nearly out of sight from North America and Europe, as
its stars extend from -46º to -60º.
(In fact it goes much further south, however except for a faint globular
cluster there's nothing of interest south of delta Ara.)
And yet this rather obscure constellation has a number of rather interesting
deep sky objects.
Gamma Arae is a fixed binary with rather faint companion: 3.5,
10; PA 328, separation 18". A second companion is twelfth magnitude: PA
66º, separation 41.6". (Burnham questions whether these form a
h4876 is a pleasant multiple in the star cluster NGC 6193 (see
below): 6.6, 8.5; 14º, 1.6"; there is a seventh magnitude
companion at PA 266º and 9.6".
h4866, better known as R Arae (see below): 6.0, 8.5; PA
The only variable of any interest in Ara is R Arae, an eclipsing binary
which changes from 6.0 to 7.0 every 4.4 days.
Deep Sky Objects:
While there are no Messier objects, several clusters are of some
NGC 6193 is a very large open cluster of about thirty stars, in
Ara, located eight degrees west of alpha Arae and one degree north
(or about seven degrees SSW of zeta Scorpii).
NGC 6397 is a bright globular cluster 2.5º NE of beta
Arae. It is only visible to those living in latitudes south of 30º
North (which means Florida in the US and none of Europe). This cluster is threeº NE of beta Arae, or forty arc minutes east of epsilon Arae.
For a closer appreciation of Ara, visit the Binocular Section.